Rubber spring devices have been conventionally used as a suspension for an off-road truck. As an example of the rubber spring devices, a rubber spring device disclosed in Patent Document 1 according to the applicant of the invention is proposed. The rubber spring device disclosed in Patent Document 1 is cited as Related Art 1 of the invention. FIG. 9 shows a front view of the rubber spring device according to Patent Document 1.
In a rubber spring device 50 shown in FIG. 9, a columnar laminated structure 51 is formed by alternately laminating a plurality of layers of hard plates 52 and rubber layers 53 (53a to 53m) between a pair of rigid end members 55, 56. A columnar cavity portion 54 penetrating in the laminating direction is formed in a central portion of the laminated structure 51. Connecting means 59 for connecting the pair of rigid end members 55, 56 is provided in the cavity portion 54.
The rubber layer 53m disposed on the side of the rigid end member 56 is formed with a thickness greater than that of the rubber layer 53a disposed on the side of the rigid end member 55.
That is, the rubber layers 53a to 53m in a middle portion of the laminated structure 51 are formed to gradually decrease in thickness stepwise toward the side of the rigid end member 55 from the side of the rigid end member 56, i.e., toward the thickness of the rubber layer 53a disposed on the side of the rigid end member 55 from the thickness of the rubber layer 53m disposed on the side of the rigid end member 56. Such a structure makes it possible to generate a substantially uniform stress in a low stress state in each of the rubber layers 53a to 53m, even when the rubber spring device 50 is deformed into an accordion shape.